The present invention relates to electronic circuits, and more particularly to detection of peak levels of a voltage signal used in such circuits.
As is known, a peak detector is an analog circuit adapted to detect the peak levels of a signal. A peak detector with a reset capability is commonly referred to as an envelop detector. Envelope detectors are widely used in gain control and spectral energy estimation. Many of the conventional peak detectors or envelope detectors (collectively and alternatively referred to hereinbelow as peak detector) can only operate at low to middle frequency bands, e.g., 1 kHz to 10 kHz, and low to middle data rate applications.
Other conventional peak detectors designed to operate at higher frequencies have a number of shortcomings. Among these shortcomings are relatively high sensitivity to temperature, and fabrication process variations. Furthermore, because such detectors often use MOS transistors that operate in subthreshold regions, their peak detection performance is highly dependent on the waveform of the signal they receive. Accordingly, these detectors also have a relatively high sensitivity to the signal waveform, as described further below.
A conventional high-speed peak detector using MOS transistors operating in subthreshold regions may accurately detect peak level P0 of signal S1, as shown in FIG. 1. However, for a signal that remains unchanged even temporarily after reaching its peak, such as signal S2 shown in FIG. 2, such conventional peak detectors detect a peak level P2 that often overshoots the actual peak level P3. The amount of overshoot ΔP is dependent, in addition to the signal waveform, on the temperature and process variations.
FIG. 3 is a schematic diagram of a peak detector 10, as known in the prior art. Transistors M2 and M3 form a current discharge path that discharge node PV carrying the detected peak voltage. Because this discharge path is slow, peak detector 10 fails to detect some of the peak levels of signal Vin. FIG. 4 shows a typical waveform of signal Vin received by peak detector 10. Because of its slow discharge path, peak detector 10 may only detect peaks P4 and P7 and thus fail to detect peaks P5 and P6. Peak detector 10 is then inoperative in applications such as high-speed optical storage applications, e.g., DVD read/write drivers that require nearly all peaks to be detected. Accordingly, a need continues to exist for a peak detector adapted to operate at relatively high frequencies, and that has a minimized sensitivity to temperature, process and waverform variations.